In the MU (Main Unit)/RRU (Remote Radio Unit) structure of a radio system, such as a cellular radio system and in particular a Time Division Synchronous Code Division Multiple Access (TD-SCDMA) radio system, a fiber is used to connect the MU and RRU. In CPRI (Common Public Radio Interface), it is also called REC (Radio Equipment control)/RE (Radio Equipment). The data transfer in the fiber follows the Ir or the CPRI specification, which includes the user-plane data, i.e., typically the digital baseband (IQ) data for different antenna-carriers (A×C). The IQ data is the chip level symbols after spreading, which is combining multi-code signal including power and weights factor information. The signal is quantized to a few bits, normally 16 bits.
In FIG. 1 the structure of the MU/RRU is depicted.
Different antenna-carriers (A×C) transport different data. Due to the limitation of fiber capacity, the 2.5 Gbps fiber can only support the data for 48 A×C. (8 antenna and 6 carriers). Currently China Mobile Communication Corporation CMCC requires that 9 carriers or 12 carriers can be supported, which can not support by 2.5 Gbps fiber.
To solve the limitation of fiber capacity, a few solutions have been proposed:
1. Use a high speed fiber (3.7 G or 5 G)
2. Use 2 2.5 Gbps fiber
3. Automatic Gain Control (AGC) is used for the IQ data. (The IQ bit-length can be reduced from 16 to 10).
The first solution is very expensive with high speed fiber. The cost of the second solution will be doubled. Simulation shows that the third solution has little effect in the uplink performance. The down link (DL) performance (such as EVM, PCDE) of the third solution will be affected. The solution can not support 12 carriers.
Hence there exists a need for an improved method and device that can meet the above requirements.